Distributed sensor fire alarm systems are known and have been found to be very useful in protecting and providing fire warnings in large structures. For example, one such system is disclosed in U.S. Pat. No. 4,916,432 to Tice, et al. entitled "Smoke And Fire Detection System Communication" assigned to the Assignee of the present invention and incorporated herein by reference.
Known systems provide a plurality of spaced-apart detector units which are linked by a bidirectional communication line to a remote control element. It has been found that the use of serial communications lines, as opposed to parallel lines, is especially desirable. Serial line costs less than does multiple conductor parallel line. In addition, the cost of installation of the serial lines can be substantially less than the cost of installation of parallel lines.
In such systems, the remotely located detecting units each are usually assigned an address. The control element is able to address each of the units in the system either on a systematic or a random basis. Alternately, the units can be polled on a round-robin basis.
Where large numbers of detector units are coupled to the control element via a bidirectional serial communication line, the time to address or poll every one of the units can start to be substantial. Situations can develop wherein with large numbers of devices, on the order of 200 or more, the time to poll all of the units can exceed 4 or 5 seconds.
In addition, in instances where some of the units are so-called control units which carry out functions other than sensing or detecting ambient conditions, it may be necessary to send multiple commands or information to each of those units to effect the desired function. This too can have an adverse effect on total polling time as the number of detectors does not necessarily decrease with the addition of extra control units.
Thus, there continues to be a need for a way to rapidly address large numbers of remote electrical units. Further, there is a need for high speed address schemes wherein the advantages of serial bidirectional communication links are not lost.
Preferably, a high-speed addressing scheme could still utilize serial bidirectional communication links. Further, it would be desirable if such a scheme or system could be implemented without adding significant cost to the control element or to the displaced detector or control units. Preferably, the scheme could be implemented with a hardware installation at the control element and with minimal or no changes to the detector units.